A voice broadcasting system which includes gain requires some means for preventing feedback from output to input in order to avoid unwanted echoes and/or oscillation. Conventional telephones achieve this by placing the speaker and microphone such that they are acoustically de-coupled from one another. As such, conventional telephones operate in the "full duplex" mode, i.e., both parties may speak at once and if both parties do speak at once, each party may hear what the other party is saying.
Speakerphones cannot acoustically de-couple the microphone and the speaker from one another. It is thus desirable operate speakerphones in the half-duplex mode, i.e., to switch the speakerphone from transmit mode to receive mode such that the speakerphone is either transmitting or receiving, but not both, at any one time. This is often accomplished by a voice-operated switch or VOX. Operation of such switches sometimes provides a "choppy" sound to the conversation by switching with inappropriate frequency or in response to background noise.
What are needed are methods and apparatus for providing hands-free conversation capabilities for speakerphones which operate well despite presence of background noise and which switch smoothly from transmit to receive and vice-versa in response to speech signals.